Project 56 - 1955/56 Operation Project 56 was a series of 4 nuclear tests conducted by the US in 1955 and 1956 the Nevada Test Site. These were safety tests, the purpose of which was to determine whether a weapon or warhead damaged in an accident would detonate with a nuclear yield, even if some or all of the high explosive components burned or detonated. The procedure was to intentionally create a fault with test bomb by removing or modifying components, and then to fire the weapon normally. If there was any nuclear yield, the test was deemed a failure. A successful test will measure only the chemical explosive in the test bomb exploding, which of course still radioactive material over a wide area. Over 3.6 square kilometres of Area 11 at the NTS were contaminated with plutonium dust and fragments. The area has become known as Plutonium Valley, and is still used for exercises in radiologically contaminated environments. The Tests Project 56 No. 1 One-point safety test of an all-oralloy prototype sealed pit weapon that was similar to the Plumbbob Priscilla and Redwing Lacrosse devices (tested at 37 and 40 kt respectively), probably the primary for the TX-15/39 and W-27. To ensure safety of the deployed design, two changes were made to enhance the nuclear output of this test. More oralloy was used than would be present in the war-reserve model. Also 3 external neutron sources ("zippers") were used to ensure a large neutron population at the moment of criticality. The device was 94cm in diameter and weighed 272kg. Project 56 No. 2 One-point safety test of the plutonium containing W-25 sealed pit weapon. The device was 44cm in diameter, 67cm long, and weighed 99kg. 3 zippers were used as neutron sources. Project 56 No. 3 This was a one-point safety test for the prototype TX/W-28 primary. The 43cm diameter nuclear system weighed 65kg, the total device weighed 125kg. 3 zippers were used as neutron sources. Project 56 No. 4 Like shot No. 3 this was a one-point safety test for the prototype TX/W-28 primary. The device was basically identical except that 6 zippers were used as neutron sources. The enhanced yield (compared to No. 3) was probably due to the larger neutron population injected into the core. Due to the low rate of neutron multiplication possible in this slightly supercritical system, only a limited amount of neutron multiplication is possible while the core remains compressed. A larger initial neutron population results in a larger final neutron population (and thus total fission output). - Click on a thumbnail for a larger version